Composition and slurry useful for metal CMP

ABSTRACT

A chemical mechanical polishing composition comprising an oxidizing agent and at least one catalyst having multiple oxidation states, the composition being useful when combined with an abrasive or with an abrasive pad to remove metal layers from a substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a chemical mechanical polishing slurry includingat least one oxidizer and a catalyst. The chemical mechanical polishingslurry is useful alone or in combination with other chemicals andabrasives for polishing metal layers and thin-films associated withsemiconductor manufacturing. More particularly this invention concerns achemical mechanical polishing slurry that is especially adapted forpolishing multiple metal layers and thin-films where one of the layersor films is comprised of tungsten and another layer or thin film iscomprised of titanium or a titanium containing alloy such as titaniumnitride.

2. Description of the Related Art

Integrated circuits are made up of millions of active devices formed inor on a silicon substrate. The active devices, which are initiallyisolated from one another, are united to form functional circuits andcomponents. The devices are interconnected through the use of well-knownmultilevel interconnections. Interconnection structures normally have afirst layer of metallization, an interconnection layer, a second levelof metallization, and sometimes a third and subsequent levels ofmetallization. Interlevel dielectrics such as doped and undoped silicondioxide (SiO₂), are used to electrically isolate the different levels ofmetallization in a silicon substrate or well. The electrical connectionsbetween different interconnection levels are made through the use ofmetallized vias. U.S. Pat. No. 4,789,648, which is incorporated hereinby reference, describes a method for preparing multiple metallizedlayers and metallized vias in insulator films. In a similar manner,metal contacts are used to form electrical connections betweeninterconnection levels and devices formed in a well. The metal vias andcontacts are generally filled with tungsten and generally employ anadhesion layer such as titanium nitride (TiN) and/or titanium to adherea metal layer such as a tungsten metal layer to SiO₂. At the contactlevel, the adhesion layer acts as a diffusion barrier to preventtungsten and SiO₂ from reacting.

In one semiconductor manufacturing process, metallized vias or contactsare formed by a blanket tungsten deposition followed by a chemicalmechanical polish (CMP) step. In a typical process, via holes are etchedthrough an interlevel dielectric (ILD) to interconnection lines or to asemiconductor substrate. Next, a thin adhesion layer such as titaniumnitride and/or titanium is generally formed over the ILD and is directedinto the etched via hole. Then, a tungsten film is blanket depositedover the adhesion layer and into the via. The deposition is continueduntil the via hole is filled with tungsten. Finally, the excess metal isremoved by chemical mechanical polishing (CMP) to form metal vias.Processes for manufacturing and/or CMP of ILD's are disclosed in U.S.Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.

In a typical chemical mechanical polishing process, the substrate isplaced in direct contact with a rotating polishing pad. A carrierapplies pressure against the backside of the substrate. During thepolishing process, the pad and table are rotated while a downward forceis maintained against the substrate back. An abrasive and chemicallyreactive solution, commonly referred to as a "slurry" is deposited ontothe pad during polishing. The slurry initiates the polishing process bychemically reacting with the film being polished. The polishing processis facilitated by the rotational movement of the pad relative to thesubstrate as slurry is provided to the wafer/pad interface. Polishing iscontinued in this manner until the desired film on the insulator isremoved.

The slurry composition is an important factor in the CMP step. Dependingon the choice of the oxidizing agent, the abrasive, and other usefuladditives, the polishing slurry can be tailored to provide effectivepolishing to metal layers at desired polishing rates while minimizingsurface imperfections, defects, corrosion, and erosion. Furthermore, thepolishing slurry may be used to provide controlled polishingselectivities to other thin-film materials used in current integratedcircuit technology such as titanium, titanium nitride and the like.

Typically CMP polishing slurries contain an abrasive material, such assilica or alumina, suspended in an oxidizing, aqueous medium. Forexample, U.S. Pat. No. 5,244,534 to Yu et al. reports a slurrycontaining alumina, hydrogen peroxide, and either potassium or ammoniumhydroxide that is useful to remove tungsten at predictable rates withlittle removal of the underlying insulating layer. U.S. Pat. No.5,209,816 to Yu et al. discloses a slurry comprising perchloric acid,hydrogen peroxide and a solid abrasive material in an aqueous medium.U.S. Pat. No. 5,340,370 to Cadien and Feller discloses a tungstenpolishing slurry comprising approximately 0.1M potassium ferricyanide,approximately 5 weight percent silica and potassium acetate. Acetic acidis added to buffer the pH at approximately 3.5.

Most of the currently available CMP slurries contain largeconcentrations of dissolved, ionic metallic components. As a result, thepolished substrates can become contaminated by the adsorption of chargedspecies into the interlayers. These species can migrate and change theelectrical properties of the devices at gates and contacts and changethe dielectric properties of the SiO₂ layers. These changes may reducethe reliability of the integrated circuits with time. Therefore, it isdesirable to expose the wafer only to high purity chemicals with verylow concentrations of mobile metallic ions.

Known, non-metallic oxidizers suffer from typically low tungstenpolishing rates. Because it is difficult to polish the tungsten at ahigh rate, the polishing step must be lengthened to remove the lasttraces of the deposited tungsten layer. Lengthening the polishing stepexposes layers, such as SiO₂, to overpolishing and to undesireableerosion. This erosion makes it more difficult to print high resolutionlines during subsequent photolithography steps increasing the number ofwafer failures. In addition, lengthened polishing steps reduce thethroughput of an IC fabrication plant and increase the cost of theresulting IC.

A new CMP slurry is, therefore, required that is both essentially freeof potential integrated circuit contaminants and that polishes at highrates.

SUMMARY OF THE INVENTION

The present invention is directed to a single chemical mechanicalpolishing composition that is essentially metal free in that it willgenerally include less than about 3000 ppm of metals or metal ions. Sucha metal free chemical mechanical polishing composition will producepolished substrates with fewer defects that are generally attributed tothe presence of metals and metal contaminants in CMP slurries.

In addition, the chemical mechanical polishing composition of thisinvention is able to polish tungsten, titanium, and titanium nitridelayers at high rates.

This invention is also a chemical mechanical polishing composition thatpresents fewer disposal problems due to its very low metals content.

In addition, this invention is a state-of-the-art chemical mechanicalpolishing composition that is able to polish tungsten at very high rateswith minimal impurity defects and that can be easily disposed of onceused.

Furthermore, this invention is directed to methods for using thechemical mechanical polishing composition of this invention in a slurryto polish a plurality of metal layers in an integrated circuit.

In one embodiment, this invention is a chemical mechanical polishingcomposition comprising an oxidizing agent and at least one catalysthaving multiple oxidation states.

In another embodiment, this invention is a chemical mechanical polishingslurry comprising an abrasive, ferric nitrate, and from about 1.0 toabout 10.0 weight percent of an oxidizing agent selected from the groupconsisting of hydrogen peroxide and monopersulfate. When the oxidizingagent is hydrogen peroxide, then the slurry includes from about 0.01 toabout 0.05 weight percent ferric nitrate. When the oxidizing agent ismonopersulfate, then the slurry includes from about 0.1 to about 0.5weight percent ferric nitrate.

In still another embodiment, this invention is a method for polishing asubstrate, including at least one metal layer, comprising the steps ofpreparing CMP slurry by admixing at least one abrasive, at least oneoxidizing agent, at least one catalyst having multiple oxidation statesand deionized water. Next, the CMP slurry is applied to the substrate,and at least a portion of the metal layer is removed from the substrateby bringing a pad into contact with the substrate.

In yet another embodiment, this invention is a method for polishing asubstrate including a tungsten layer. The method is accomplished bypreparing a CMP slurry by admixing from about 1.0 to about 15.0 weightpercent silica, from about 0.01 to about 1.0 weight percent ferricnitrate, from about 1.0 to about 10 weight percent of an oxidizing agentselected from the group consisting of hydrogen peroxide, monopersulfatesand mixtures thereof, and deionized water. Next, the chemical mechanicalpolishing slurry is applied to the substrate, and at least a portion ofthe tungsten layer is removed from the substrate by bringing a pad intocontact with the substrate and moving the pad in relation to thesubstrate.

In another embodiment, this invention is a multi-package system usefulfor preparing a chemical mechanical polishing slurry. The multiplepackage system includes a first container comprising at least oneoxidizing agent and a second container comprising at least one catalysthaving multiple oxidation states.

DESCRIPTION OF THE CURRENT EMBODIMENT

The present invention relates to a chemical mechanical polishingcomposition that comprises at least one oxidizer and at least onecatalyst that promotes a chemical reaction between the oxidizer and asubstrate metal layer. The chemical mechanical polishing composition isused to polish at least one metal layer associated with a substrateselected from the group including silicon substrates, TFT-LCD glasssubstrates, GaAs substrates, and other substrates associated withintegrated circuits, thin films, multiple level semiconductors, andwafers. In particular, the chemical mechanical polishing slurry of thisinvention has been found to exhibit excellent polishing performance whenused to polish a substrate including one or more layers of tungsten,titanium, and titanium nitride in a single step, multiple metal layerchemical mechanical polishing process.

Before describing the details of the various preferred embodiments ofthis invention, some of the terms that are used herein will be defined.The "chemical mechanical composition" refers to the combination of atleast one oxidizer and at least one catalyst that may be used inconjunction with an abrasive pad to remove one or more layers of metalfrom a multiple layer metallization.

The term chemical mechanical polishing slurry, ("CMP slurry"), refers toanother useful product of this invention that comprises the chemicalmechanical composition of this invention and at least one abrasive. TheCMP slurry is useful for polishing a multiple level metallization whichmay include but are not limited to semi-conductor thin-films, integratedcircuit thin-films, and for polishing any other films, surfaces andsubstrates where CMP processes are useful.

One aspect of this invention is a chemical mechanical compositioncomprising an oxidizing agent and catalyst that is useful in oxidizingmetal layers in polishing applications. This chemical mechanicalcomposition is useful when incorporated in a chemical mechanicalpolishing slurry to oxidize a metal layer to its corresponding oxide orions. For example, the combination can be used to oxidize tungsten totungsten oxide, aluminum to aluminum oxide and copper to copper oxide.The oxidizing agent--catalyst combinations disclosed herein are usefulwhen incorporated into a CMP slurry or when used alone in conjunctionwith an abrasive pad to polish metals and metal based componentsincluding tungsten, titanium, titanium nitride, copper, aluminum andvarious mixtures and combinations thereof.

The chemical mechanical composition of this invention includes at leastone oxidizing agent that has an electrochemical potential greater thanthe electrochemical potential necessary to oxidize the catalyst. Forexample an oxidizing agent having a potential of greater than 0.771volts versus normal hydrogen electrode is necessary when a hexa aquairon catalyst is oxidized from Fe(II) to Fe(III). If an aqua coppercomplex is used, an oxidizing agent having a potential of greater than0.153 volts versus normal hydrogen electrode is necessary to oxidizeCu(I) to CU(II). These potentials are for specific complexes only, andmay change, as will the useful oxidizers, upon the addition of additivessuch as ligands (complexing agents) to the compositions of thisinvention.

The oxidizing agent is preferably an inorganic or organic per-compound.A per-compound as defined by Hawley's Condensed Chemical Dictionary is acompound containing at least one peroxy group (--O--O--) or a compoundcontaining an element in its highest oxidation state. Examples ofcompounds containing at least one peroxy group include but are notlimited to hydrogen peroxide and its adducts such as urea hydrogenperoxide and percarbonates, organic peroxides such as benzoyl peroxide,peracetic acid, and di-t-butyl peroxide, monopersulfates (SO₅.sup.═),dipersulfates (S₂ O₈.sup.═), and sodium peroxide. Examples of compoundscontaining an element in its highest oxidation state include but are notlimited to periodic acid, periodate salts, perbromic acid, perbromatesalts, perchloric acid, perchloric salts, perboric acid, and perboratesalts and permanganates. Examples of non-per compounds that meet theelectrochemical potential requirements include but are not limited tobromates, chlorates, chromates, iodates, iodic acid, and cerium (IV)compounds such as ammonium cerium nitrate.

The most preferred oxidizing agents are hydrogen peroxide and itsadducts, and monopersulfates. Monopersulfates are compounds whichinclude the oxidizing SO₅.sup.═ group as shown below. ##STR1## where X₁and X₂ are each individually H₁, Si(R')₃, NH₄, N(R")₄ and alkali earthmetals such as Li, Na, K, and so forth; where R' is an alkyl grouphaving from 1 to 10 or more carbon atoms, and wherein R" is H, an alkylgroup, an aryl group, or mixtures thereof including, for example, NMe₄,NBu₄, NPh₄, NMeBu₃, NHEt₃ and so forth. One wellknown and preferredclass of monopersulfates are combinations of KHSO₅, KHSO₄ and K₂ SO₄.This combination is known as a triple salt.

The oxidizing agent may be present in the overall chemical mechanicalpolishing slurry in an amount ranging from about 0.5 to about 50.0weight percent. It is preferred that the oxidizer is present in theslurry in an amount ranging from about 1.0 to about 10.0 weight percent.

The chemical mechanical composition of this invention includes at leastone catalyst. The purpose of the catalyst is to transfer electrons fromthe metal being oxidized to the oxidizer (or analogously to transferelectrochemical current from the oxidizer to the metal). The catalyst orcatalysts chosen may be metallic, non-metallic, or a combination thereofand the catalyst must be able to shuffle electrons efficiently andrapidly between the oxidizer and metal substrate surface. Preferably,the catalyst is chosen from metal compounds that have multiple oxidationstates, such as but not limited to Ag, Co, Cr, Cu, Fe, Mo, Mn, Nb, Ni,Os, Pd, Ru, Sn, Ti and V. The term "multiple oxidation states" refers toan atom and/or compound that has a valence number that is capable ofbeing augmented as the result of a loss of one or more negative chargesin the form of electrons. Most preferred metal catalysts are compoundsof Ag, Cu and Fe and mixtures thereof. Especially preferred are ironcatalysts such as but not limited to inorganic salts of iron, such asiron (II or III) nitrate, iron (II or III) sulfate, iron (II or III)halides, including fluorides, chlorides, bromides, and iodides, as wellas perchlorates, perbromates and periodates, and ferric organic iron (IIor III) compounds such as but not limited to acetates, acetylacetonates,citrates, gluconates, oxalates, phthalates, and succinates, and mixturesthereof.

The catalyst may be present in the chemical mechanical polishingcomposition in an amount ranging from about 0.001 to about 2.0 weightpercent. It is preferred that the catalyst will be present in thechemical mechanical polishing composition in an amount ranging fromabout 0.005 to about 0.5 weight percent. At this preferred catalystloading level, i.e., 0.5 weight percent or less, and when a non-metallicoxidizing agent such as hydrogen peroxide, urea hydrogen peroxide ormonopersulfate is used, the chemical mechanical polishing composition isessentially metal and "metallic ion free" in comparison to commerciallyavailable ferric nitrate based slurries.

The amount of catalyst in the chemical mechanical composition of thisinvention may be varied depending upon the oxidizing agent used. Whenthe preferred oxidizing agent hydrogen peroxide is used in combinationwith a preferred catalyst such as ferric nitrate, the catalyst willpreferably be present in the composition in an amount ranging from about0.005 to about 0.20 weight percent (approximately 7 to 280 ppm Fe insolution). When the preferred oxidizing agent is a triple salt ofmonopersulfate and a preferred catalyst such as ferric nitrate is used,the catalyst will preferably be present in the composition in an amountranging from about 0.05 to about 1.0 weight percent (approximately 70 toabout 1400 ppm Fe in solution).

The concentration ranges of catalyst in the chemical mechanicalpolishing slurry of this invention are generally reported as a weightpercent of the entire compound. The use of high molecular weight metalcontaining compounds that comprise only a small percentage by weight ofcatalyst is well within the scope of catalysts in this invention. Theterm catalyst when used herein also encompasses compounds wherein thecatalytic metal comprises less than 10% by weight of the metal in thecomposition and wherein the metal catalyst concentration in the CMPslurry is from about 2 to about 3000 ppm of the overall slurry weight.

The chemical mechanical composition of this invention may be combinedwith at least one abrasive to produce a CMP slurry. The abrasive istypically a metal oxide abrasive. The metal oxide abrasive may beselected from the group including alumina, titania, zirconia, germania,silica, ceria and mixtures thereof. The CMP slurry of this inventionpreferably includes from about 1.0 to about 20.0 weight percent or moreof an abrasive. It is more preferred, however, that the CMP slurry ofthis invention includes from about 3.0 to about 6.0 weight percentabrasive.

The metal oxide abrasive may be produced by any techniques known tothose skilled in the art. Metal oxide abrasives can be produced usingany high temperature process such as sol-gel, hydrothermal or, plasmaprocess, or by processes for manufacturing fumed or precipitated metaloxides. Preferably, the metal oxide is a fumed or precipitated abrasiveand, more preferably it is a fumed abrasive such as fumed silica orfumed alumina. For example, the production of fumed metal oxides is awell-known process which involves the hydrolysis of suitable feedstockvapor (such as aluminum chloride for an alumina abrasive) in a flame ofhydrogen and oxygen. Molten particles of roughly spherical shapes areformed in the combustion process, the diameters of which are variedthrough process parameters. These molten spheres of alumina or similaroxide, typically referred to as primary particles, fuse with one anotherby undergoing collisions at their contact points to form branched, threedimensional chain-like aggregates. The force necessary to breakaggregates is considerable and often considered irreversible. Duringcooling and collecting, the aggregates undergo further collision thatmay result in some mechanical entanglement to form agglomerates.Agglomerates are thought to be loosely held together by van der Waalsforces and can be reversed, i.e., de-agglomerated, by proper dispersionin a suitable media.

Precipitated abrasives may be manufactured by conventional techniquessuch as by coagulation of the desired particles from an aqueous mediumunder the influence of high salt concentrations, acids or othercoagulants. The particles are filtered, washed, dried and separated fromresidues of other reaction products by conventional techniques known tothose skilled in the art.

A preferred metal oxide will have a surface area, as calculated from themethod of S. Brunauer, P. H. Emmet, and I. Teller, J. Am. ChemicalSociety, Volume 60, Page 309 (1938) and commonly referred to as BET,ranging from about 5 m² /g to about 430 m² /g and preferably from about30 m² /g to about 170 m² /g. Due to stringent purity requirements in theIC industry the preferred metal oxide should be of a high purity. Highpurity means that the total impurity content, from sources such as rawmaterial impurities and trace processing contaminants, is typically lessthan 1% and preferably less than 0.01% (i.e., 100 ppm).

In this preferred embodiment, the metal oxide abrasive consists of metaloxide aggregates having a size distribution less than about 1.0 micron,a mean aggregate diameter less than about 0.4 micron and a forcesufficient to repel and overcome the van der Waals forces betweenabrasive aggregates themselves. Such metal oxide abrasive has been foundto be effective in minimizing or avoiding scratching, pit marks, divotsand other surface imperfections during polishing. The aggregate sizedistribution in the present invention may be determined utilizing knowntechniques such as transmission electron microscopy (TEM). The meanaggregate diameter refers to the average equivalent spherical diameterwhen using TEM image analysis, i.e., based on the cross-sectional areaof the aggregate. By force is meant that either the surface potential orthe hydration force of the metal oxide particles must be sufficient torepel and overcome the van der Waals attractive forces between theparticles.

In another preferred embodiment, the metal oxide abrasive may consist ofdiscrete, individual metal oxide particles having a primary particlediameter less than 0.4 micron (400 nm) and a surface area ranging fromabout 10 m² /g to about 250 m² /g.

Preferably, the metal oxide abrasive is incorporated into the aqueousmedium of the polishing slurry as a concentrated aqueous dispersion ofmetal oxides, which concentrated aqueous dispersion of metal oxideabrasives typically ranges from about 3% to about 45% solids, andpreferably between 10% and 20% solids. The aqueous dispersion of metaloxides may be produced utilizing conventional techniques, such as slowlyadding the metal oxide abrasive to an appropriate media, for example,deionized water, to form a colloidal dispersion. The dispersion istypically completed by subjecting it to high shear mixing conditionsknown to those skilled in the art. The pH of the slurry may be adjustedaway from the isoelectric point to maximize colloidal stability.

Other well known polishing slurry additives may be incorporated alone orin combination into the chemical mechanical polishing slurry of thisinvention. A non-inclusive list is inorganic acids, organic acids,surfactants, alkyl ammonium salts or hydroxides, and dispersing agents.

An additive which may be useful with this invention is one whichstabilizes the oxidizer in the presence of the metal complex. It is wellknown that hydrogen peroxide is not very stable in the presence of manymetal ions without the use of stabilizers. Useful stabilizers includephosphoric acid, organic acids (e.g., acetic, citric, tartaric,orthophthalic, and EDTA), tin oxides, phosphonate compounds and otherligands which bind to the metal and reduce its reactivity towardhydrogen peroxide decomposition. These additives can be used alone or incombination and significantly decrease the rate at which hydrogenperoxide decomposes, and may also effect tungsten polishing rates.

The chemical mechanical polishing composition of this invention has beenfound to have a high tungsten (W) polishing rate as well as goodpolishing rates towards titanium (Ti). In addition, the chemicalmechanical polishing composition exhibits desirable low polishing ratestowards the dielectric insulating layer.

The composition of this invention may be produced using any techniquesknown to those skilled in the art. Typically, the oxidizing agent andcatalyst are mixed into the aqueous medium, such as deionized ordistilled water, at pre-determined concentrations under low shearconditions until such components are completely dissolved in the medium.A concentrated dispersion of the metal oxide abrasive, such as fumedsilica, is added to the medium and diluted to the desired loading levelof abrasive in the final CMP slurry. In addition, the catalyst may beadded to the slurry by any method that is able to incorporate metalcatalytic compounds of this invention in an aqueous solution.

The compositions of the present invention may be supplied as one packagesystem (at least one oxidizing agent, at least one catalyst, optionalabrasive, and optional additives in a stable aqueous medium). To avoidpossible composition degradation, however, it is preferred that at leasta two package system is used where the first package comprises at leastone oxidizing agent, and the second package comprises at least onecatalyst. Optional components, such as an abrasive and any optionaladditives may be placed in either the first container, the secondcontainer or in a third container. Furthermore, the components in thefirst container or second container may be in dry form while thecomponents in the corresponding container are in the form of an aqueousdispersion. For example, the first container may comprise an oxidizer,such as hydrogen peroxide, in liquid form while the second containercomprises a catalyst, such a ferric nitrate, in dry form. Alternately,the first container may comprise a dry oxidizing agent while the secondcontainer may comprise an aqueous solution of at least one catalyst.Other two-container, and three or more container combinations of theingredients of the chemical mechanical composition and CMP slurry ofthis invention are within the knowledge of one having ordinary skill inthe art.

A multi-package chemical mechanical composition or CMP slurry may beused with any standard polishing equipment appropriate for use on thedesired metal layer of the wafer. The multi-package system includes oneor more CMP components in aqueous or dry form in two or more containers.The multi-package system is used by combining the components from thevarious containers in the desired amounts to give a CMP slurrycomprising at least one oxidizing agent, at least one catalyst, and anoptional abrasive in amounts described above.

EXAMPLES

We have discovered that a composition including an oxidizer and acatalyst is capable of polishing a multiple metal layer comprisingtungsten and titanium at high rates while exhibiting an acceptable lowpolishing rate towards the dielectric layer.

The following examples illustrate preferred embodiments of thisinvention as well as preferred methods for using compositions of thisinvention.

EXAMPLE 1

Polishing slurries were prepared in order to evaluate the performance ofthe resulting CMP slurries on tungsten wafer CMP. Performance parametersmeasured included tungsten polishing rates. A standard abrasive slurryincluding 5.0 weight percent colloidal silica and deionized water wasused for all runs. Various oxidizing agents and catalysts were added tothe standard abrasive slurry in order to evaluate the effect of variousCMP slurry compositions on tungsten polishing rates. The polishingslurries were prepared by combining appropriate amounts of SCE, a fumedsilica-based dispersion manufactured by Cabot Corporation and sold underthe trademark CAB-O-SPERSE® with the recited amounts of oxidizing agent,catalyst, and, if appropriate, additional additives.

The CMP slurries were applied to chemically-mechanically polish tungstenblanket wafers having thickness of approximately 8000 Å using a SUBA500/SUBA IV pad stack manufactured by Rodel, Inc. The polishing wasperformed using a IPEC/WESTECH 472 CMP tool for one minute at a downforce of 5 psi, a slurry flow rate of 150 ml/min, a table speed of 60rpm, and a spindle speed of 65 rpm.

EXAMPLE 2

Five polishing slurries were prepared according to the method of Example1 to investigate the effect of the addition of a ferric nitratecatalyst, and/or a hydrogen peroxide oxidizing agent to a CMP slurry ontungsten rates. Each slurry included 5.0 wt % fumed silica. Theconcentrations of hydrogen peroxide and ferric nitrate in each slurryare indicated in Table 1.

                  TABLE 1    ______________________________________                        Ferric Nitrate                                   W CMP Rate    Slurry  H.sub.2 O.sub.2 wt %                        wt %       Å/min    ______________________________________    1       0           0           43    2       0           0.2         291    3       5.0         0           385    4       5.0         0.02       4729    5       5.0         0.05       6214    ______________________________________

As shown in Table 1, the control samples (slurries 1-3) polish tungstenat unacceptably low rates. In particular, neither hydrogen peroxidealone nor catalytic amounts of ferric nitrate alone achieve significanttungsten rates. Slurries 4 and 5, however, demonstrate that when anoxidizing agent and a catalyst are used in combination, there is astrong synergistic effect that results in tungsten rates on the order of5000 Å/min and greater. The addition of catalytic amounts of ferricnitrate to hydrogen peroxide (or conversely the addition of hydrogenperoxide to ferric nitrate) results in greater than one order ofmagnitude increase in tungsten rates.

EXAMPLE 3

Five polishing slurries were prepared and tested according to themethods set forth in Example 1 in order to investigate the effect of theaddition of ferric nitrate catalyst and/or monopersulfate oxidizingagent to a CMP slurry on tungsten chemical mechanical polishing rates.The source of monopersulfate used in this Example is Oxone® manufacturedby DuPont. Oxone® consists of the triple salt: 2KHSO₅.KHSO₄.K₂ SO₄, andis approximately 50% monopersulfate by weight. Each slurry included 5.0wt % fumed silica. The concentrations of ferric nitrate andmonopersulfate in the slurries are set forth in Table 2 below.

                  TABLE 2    ______________________________________                         Ferric nitrate                                   W CMP Rate    Slurry  Oxone ® wt %                         wt %      Å/min    ______________________________________    1       0.0          0.0        43    2       0.0          0.2        291    3       10.0         0.0        264    4       20.0         0.0        413    5       10.0         0.2       3396    ______________________________________

As shown in Table 2, the control samples, (slurries 1-4), polishtungsten at unacceptably low rates. Slurry 5, a combination of 5.0 wt. %monopersulfate and 0.2 wt. % ferric nitrate catalyst was able to polisha tungsten layer at a very high rate, once again demonstrating thesynergistic effect of combining an electron shuffling catalyst with anoxidizing agent that has an electrochemical potential greater than thepotential necessary to oxidize the catalyst.

EXAMPLE 4

Eight polishing slurries, each including varying amounts of hydrogenperoxide and ferric nitrate were prepared and tested according to themethods set forth in Example 1. Each slurry included 5.0 wt % fumedsilica. The concentrations of ferric nitrate and hydrogen peroxide inthe slurries are set forth in Table 3 below.

                  TABLE 3    ______________________________________                        Ferric Nitrate                                   W CMP Rate    Slurry  H.sub.2 O.sub.2 wt %                        wt %       Å/min    ______________________________________    1       0.1         0.20        717    2       1.0         0.05       2694    3       2.0         0.02       3019    4       3.0         0.01       2601    5       3.0         0.02       3420    6       3.0         0.05       4781    7       5.0         0.01       3374    8       5.0         0.02       4729    9       5.0         0.05       6214    ______________________________________

As shown in Table 3, tungsten polishing rates vary depending upon boththe amount of hydrogen peroxide and the amount of ferric nitratecatalyst in the slurry. Furthermore, the results reported in Table 3also demonstrate that only a very small amount of catalyst--0.05 weightpercent or less--is very effective in catalyzing tungsten polishingusing a CMP slurry comprising hydrogen peroxide.

EXAMPLE 5

Nine polishing slurries were prepared and tested according to themethods set forth in Example 1 in order to investigate the effect ofvarying the amount of ferric nitrate catalyst and/or monopersulfate(Oxone®) oxidizing agent in a CMP slurry on tungsten chemical mechanicalpolishing rates. Each slurry included 5.0 wt % fumed silica. Theconcentrations of ferric nitrate and monopersulfate in the slurries areset forth in Table 4 below.

                  TABLE 4    ______________________________________            Oxone ® Ferric Nitrate                                   W CMP Rate    Slurry  wt %        wt %       Å/min    ______________________________________    1       5.0         0.05       1925    2       5.0         0.14       2921    3       5.0         0.2        3178    4       5.0         0.35       3401    5       10.0        0.036      1661    6       10.0        0.2        3396    7       10.0        0.5        3555    8       15.0        0.05       2107    9       15.0        0.35       3825    ______________________________________

The results of the tungsten CMP reported in Table 4 demonstrates thatvarying the amount of monopersulfate in the CMP slurry has a lessereffect on tungsten polishing rates than varying the amount of catalystin the CMP slurry.

EXAMPLE 6

Eleven CMP slurries were prepared and tested according to the method setforth in Example 1 in order to investigate the effect of varying thecatalyst type and oxidizing agent type on tungsten chemical mechanicalpolishing rates. Each slurry included 5.0 wt % fumed silica. The typeand concentrations of catalyst and oxidizing agent used in each CMPslurry are set forth in Table 5 below.

                  TABLE 5    ______________________________________                                   W CMP Rate    Slurry  Oxidizer wt %                        Catalyst wt %                                   Å/min    ______________________________________     1      5.0% H.sub.2 O.sub.2                         28 ppm Cu 1417     2      5.0% H.sub.2 O.sub.2                         70 ppm Cu,                                   2134                         7 ppm Fe     3      5.0% H.sub.2 O.sub.2                         28 ppm Ag  561     4      5.0% H.sub.2 O.sub.2                         28 ppm Fe 4729     5      5.0% Oxone ®                        560 ppm Cu 1053     6      5% Oxone ®                        700 ppm Ag  608     7      5.0% Oxone ®                        280 ppm Fe 3178     8      5.0% (NH.sub.4).sub.2 S.sub.2 O.sub.8                         70 ppm Cu  712     9      5.0%         70 ppm Fe 1501            (NH.sub.4).sub.2 Ce(NO.sub.3).sub.6    10      5.0% K-Iodate                         70 ppm Fe 1203    11      5.0% H.sub.2 O.sub.2,                        280 ppm Fe 7840            1.0% Oxone ®    ______________________________________

Each slurry tested exhibited tungsten polishing rates superior toslurries including only an oxidizing agent (Example 2--slurry 3; Example3--slurries 3 & 4) and superior to slurries including catalyst alone(Example 2--slurry 2; Example 3--slurry 2).

While the present invention has been described by means of specificembodiments, it will be understood that modifications may be madewithout departing from the spirit of the invention. The scope of theinvention is not to be considered as limited by the description of theinvention set forth in the specification and examples, but rather asdefined by the following claims.

For example, although the examples above have described the preparationof CMP slurries with metal catalysts, it is to be understood thatnon-metal catalysts having multiple oxidation states may be incorporatedinto useful CMP compositions and slurries of this invention.

EXAMPLE 7

Two polishing slurries were prepared in order to evaluate theirperformance on patterned device wafers. Each wafer consisted of aW/TiN/Ti metallization deposited over a patterned PETEOS layer. Theinitial W layer thickness was 8000 Å, the TiN layer 400 Å, and the Tilayer 250 Å. Each wafer was polished until the W/TiN/Ti metallizationwas cleared from the entire wafer. The polishing conditions set forth inExample 1 were used. Slurries 1 and 2 contained 5.0 weight percent fumedsilica. The type and concentrations of the catalyst and oxidizing agentused in each slurry are set forth in Table 6. A third commerciallyavailable slurry including 3 weight percent alumina abrasive and 5.0weight percent ferric nitrate was also evaluated.

                  TABLE 6    ______________________________________            Oxidizer    Slurry  (wt %)       Catalyst  Time to Clear    ______________________________________    1       5% H.sub.2 O.sub.2                          28 ppm Fe                                    90 seconds    2       5% H.sub.2 O.sub.2 & 1%                         280 ppm Fe                                    70 seconds            Oxone ®    3            Commercial Slurry -                                   170 seconds                 5 wt % Ferric Nitrate    ______________________________________

Excellent polishing performance was achieved using slurries 1 and 2. Theslurries were observed to have high polishing rates on each of themetallization layers, resulting in a minimum time to clear themetallization. Both catalyst containing slurries exhibited superiorperformance in comparison to the commercially available slurry.Examination of the polished wafers with atomic force microscopedemonstrated that the device wafers were successfully planarized, withacceptable low levels of erosion and dishing of stud and line features.Furthermore, the underlying PETEOS layer was smooth with no evidence ofscratches or pits.

What we claim is:
 1. A chemical mechanical polishing composition comprising the synergistic combination of:at least one oxidizing agent; and at least one catalyst having multiple oxidation states.
 2. A chemical mechanical polishing slurry comprising the chemical mechanical polishing composition of claim 1 and at least one abrasive.
 3. The chemical mechanical polishing composition of claim 1 wherein the oxidizing agent has an electrochemical potential greater than the electrochemical potential necessary to oxidize the catalyst.
 4. The chemical mechanical polishing composition of claim 3 wherein the oxidizing agent is an organic per compound, an inorganic per compound, a non-per compound, or mixtures thereof.
 5. The chemical mechanical polishing composition of claim 4 wherein the oxidizing agent is a monopersulfate, persulfate, peroxide, periodate or mixtures thereof.
 6. The chemical mechanical polishing composition of claim 5 wherein the oxidizing agent includes at least one monopersulfate having the formula: ##STR2## where X₁, X₂ are each individually H, Si(R')₃, NH₄, N(R")₄ and alkali earth metals such as Li, Na, K; where R' is an alkyl group having from 1 to 10 or more carbon atoms; and wherein R" is H, an alkyl group, an aryl group, or mixtures thereof.
 7. The chemical mechanical polishing composition of claim 6 including from about 0.5 to about 20 weight percent monopersulfate.
 8. The chemical mechanical polishing composition of claim 6 including from about 1 to about 20 weight percent 2KHSO₅.KHSO₄.K₂ SO₄.
 9. The chemical mechanical polishing composition of claim 5 wherein the oxidizing agent is hydrogen peroxide.
 10. The chemical mechanical polishing composition of claim 9 including from about 0.1 to about 50 weight percent hydrogen peroxide.
 11. The chemical mechanical polishing composition of claim 9 including from about 1.0 to about 10 weight percent hydrogen peroxide.
 12. The chemical mechanical polishing composition of claim 1 wherein the catalyst is a metal compound.
 13. The chemical mechanical polishing composition of claim 12 wherein the catalyst is a metal compound of Ag, Co, Cr, Cu, Fe, Mo, Mn, Nb, Ni, Os, Pd, Ru, Sn, Ti, V and mixtures thereof having multiple oxidation states.
 14. The chemical mechanical polishing composition of claim 13 wherein the catalyst is a compound of iron, copper, silver, and any combination thereof having multiple oxidation states.
 15. The chemical mechanical polishing composition of claim 14 wherein the catalyst is an iron catalyst compound selected from the group consisting of inorganic iron compounds and organic iron compounds having multiple oxidation states.
 16. The chemical mechanical polishing composition of claim 15 wherein the iron catalyst is ferric nitrate.
 17. The chemical mechanical polishing composition of claim 14 wherein the catalyst is a copper catalyst selected from the group consisting of inorganic copper compounds and organic copper compounds.
 18. The chemical mechanical polishing composition of claim 17 wherein the catalyst is copper nitrate.
 19. The chemical mechanical polishing composition of claim 14 wherein the catalyst is the combination of a copper compound and an iron compound.
 20. The chemical mechanical polishing composition of claim 1 including from about 0.001 to about 2.0 weight percent catalyst.
 21. The chemical mechanical polishing composition of claim 20 including from about 0.005 to about 0.2 weight percent catalyst.
 22. The chemical mechanical polishing composition of claim 1 wherein the oxidizing agent is hydrogen peroxide and the catalyst is from about 0.01 to about 0.5 weight percent of an iron catalyst.
 23. The chemical mechanical polishing composition of claim 1 wherein the oxidizing agent is monopersulfate and wherein the catalyst is from about 0.05 to about 1.0 weight percent of an iron catalyst.
 24. A chemical mechanical polishing slurry comprising:an abrasive; a ferric nitrate catalyst; and from about 1.0 to about 10.0 weight percent of an oxidizing agent selected from the group consisting of hydrogen peroxide and monopersulfate wherein when the oxidizing agent is hydrogen peroxide, then the slurry includes from about 0.01 to about 0.05 weight percent ferric nitrate catalyst and when the oxidizing agent is monopersulfate, then the slurry includes from about 0.1 to about 0.5 weight percent ferric nitrate catalyst.
 25. The chemical mechanical polishing slurry of claim 24 wherein the abrasive is at least one metal oxide.
 26. The chemical mechanical polishing slurry of claim 25 wherein the metal oxide abrasive is selected from the group including alumina, ceria, germania, silica, titania, zirconia, and mixtures thereof.
 27. The chemical mechanical polishing slurry of claim 24 wherein the abrasive is an aqueous dispersion of a metal oxide.
 28. The chemical mechanical polishing slurry of claim 25 wherein the metal oxide abrasive consists of metal oxide aggregates having a size distribution less than about 1.0 micron and a mean aggregate diameter less than about 0.4 micron.
 29. The chemical mechanical polishing slurry of claim 25 wherein the metal oxide abrasive consists of discrete, individual metal oxide spheres having a primary particle diameter less than 0.400 micron and a surface area ranging from about 10 m² /g to about 250 m² /g.
 30. The chemical mechanical polishing slurry of claim 24 wherein the abrasive has a surface area ranging from about 5 m² /g to about 430 m² /g.
 31. The chemical mechanical polishing slurry of claim 30 wherein the abrasive has a surface area of from about 30 m² /g to about 170 m² /g.
 32. The chemical mechanical polishing slurry of claim 24 wherein the abrasive is precipitated abrasives or fumed abrasives.
 33. The chemical mechanical polishing slurry of claim 24 wherein the abrasive is silica.
 34. The chemical mechanical polishing slurry of claim 33 wherein the abrasive is fumed silica.
 35. A chemical mechanical polishing slurry comprising:from about 1.0 to about 15.0 weight percent silica; from about 0.1 to about 0.5 weight percent ferric nitrate catalyst; and from about 1.0 to about 10.0 weight percent monopersulfate.
 36. A chemical mechanical polishing slurry comprising:from about 1.0 to about 15.0 weight percent silica; from about 0.01 to about 0.05 weight percent ferric nitrate catalyst; and from about 1.0 to about 10.0 weight percent hydrogen peroxide.
 37. A method for polishing a substrate including at least one metal layer comprising the steps of:(a) admixing at least one abrasive, at least one oxidizing agent, at least one catalyst having multiple oxidation states and deionized water to give a chemical mechanical polishing slurry; (b) applying the chemical mechanical polishing slurry to the substrate; and (c) removing at least a portion of the metal layer from the substrate by bringing a pad into contact with the substrate and moving the pad in relation to the substrate.
 38. The method of claim 37 wherein the substrate includes a tungsten containing metal layer wherein at least a portion of the tungsten layer is removed in step (c).
 39. The method of claim 38 wherein the substrate further includes a titanium and/or titanium nitride metal layer wherein at least a portion of the titanium nitride layer is removed in step (c).
 40. The method of claim 37 wherein the catalyst is selected from the group of inorganic iron compounds and organic iron compounds.
 41. The method of claim 40 wherein the catalyst is ferric nitrate.
 42. The method of claim 41 wherein the ferric nitrate catalyst is present in the slurry in an amount ranging from about 0.001 to about 2.0 weight percent.
 43. The method of claim 37 wherein the catalyst is selected from the group of inorganic copper compounds and organic copper compounds.
 44. The method of claim 37 wherein the abrasive is a metal oxide.
 45. The method of claim 44 wherein the metal oxide abrasive is selected from the group including alumina, ceria, germania, silica, titania, zirconia, and mixtures thereof.
 46. The method of claim 37 wherein the abrasive is an aqueous dispersion of a metal oxide.
 47. The method of claim 37 wherein the abrasive is selected from the group consisting of precipitated alumina, fumed alumina, precipitated silica, fumed silica, and mixtures thereof.
 48. The method of claim 37 wherein the abrasive is silica.
 49. A method for polishing a substrate including tungsten layer comprising:(a) admixing from about 1.0 to about 15.0 weight percent silica, from about 0.001 to about 2.0 weight percent ferric nitrate catalyst, from about 2.0 to about 10 weight percent of an oxidizing agent selected from the group consisting of hydrogen peroxide, monopersulfates and mixtures thereof, and deionized water to give a mechanical chemical polishing slurry; (b) applying the chemical mechanical polishing slurry to the substrate; and (c) removing at least a portion of the tungsten layer by bringing a pad into contact with the substrate and moving the pad in relation to the substrate. 